Fog-generating devices are used in several applications. They are used in entertainment for creating a specific mood or enhancing visual lighting effects. During the training of emergency and military personnel, they are used to simulate fire. In addition, they are used in security systems to disorient intruders and to hide valuables from them.
Typically, a fog-generating device creates fog by driving a fog-generating substance through a heat exchanger; upon which the fog-generating substance is converted into the vapour phase that is ejected at the exit [end] of the heat exchanger. Dependent upon the atmosphere in which said vapour is being ejected; the vapour may condense upon expansion into tiny liquid droplets suspended in the air as an aerosol, with the formation of a fog.
Thus as used herein “expel of fog” or similar terms by a fog-generating device, generally refers to the process wherein a fog-generating substance (hereinafter also referred to as a fog-generating material) is driven through a heat-exchanger, with the conversion of said fog-generating substance into the vapour phase that is ejected at the exit [end] of said heat exchanger.
Most often, a pump is used to drive fog-generating liquid from a reservoir to a heat exchanger. However, in said case, the time needed to convert all the fog-generating liquid to fog is dependent on the capacity of the pump, i.e. its ability to deliver a given flow within a given time at given pressure. Fog-generating device are often powered by standard voltage batteries, further restricting the capacity of such pumps. In addition, high-capacity liquid pumps would lead to too high product prices. Therefore, utilization of pumps to drive fog-generating liquids from the reservoir to the heat-exchanger seriously restricts the fog output of those fog-generating devices. WO2008132113 addresses this problem by using a pressure [compressed] vessel as a fog-generating liquid reservoir. When fog needs to be generated a normally closed valve (switch) between the pressure vessel and the connected heat exchanger is opened and, the pressure inside the vessel drives the fog-generating liquid from said vessel to the heat exchanger, thereby improving the capacity at which fog can be expelled from the device.
The capacity at which fog can be generated is of crucial importance when the device is used as a security device. For example, in the case of a burglary, the fog-generating device should fill the room with fog within a few seconds. In such case, valuables are immediately obscured from the sight of the intruder, and he will quickly try to escape by leaving the room. When fog is generated too slowly, the thief may use the additional seconds to quickly grasp valuables before leaving. The speed at which fog is generated by the device of WO2008132113 is dependent on the pressure in the vessel that contains the fog-generating liquid. While the pressure (P) and volume (V) that can be contained in the vessel is unlimited in theory, the legal framework on devices containing pressurized vessels restricts it's capacity. Above certain pressure thresholds and P×V, the laws make it impractical to build, transport, install and use such devices. Thus, although WO2008132113 presented a major improvement for security fog-generating devices, there is still a need for devices for faster fog generation, e.g. to more quickly fill a room with fog or to fill larger rooms with fog in the same time-frame.
It has been found that the fog-generators of the present invention solve the above-mentioned problems and allow a much faster generation of fog, due to the high entrance pressure that can be generated at the heat exchanger. Detailed analysis showed that prior art devices using a pump typically provide about 6 ml/s of fog-generating fluid to the heat exchanger at about 4-6 bar. Prior art devices which use a propellant gas to drive the fluid typically operate at about 28 ml/s at about 12-15 bar. Remarkably, a fog-generating device of the present invention comprising a removable housing with a pyrotechnic device have been found to be easily able to provide 60-80 ml/s of fluid to the heat exchanger at about 300-400 bar.
Prior art fog-generating devices for security purposes have another inherent risk. In contrast to fog-generating devices for entertainment, for military use and for training emergency personnel, fog-generating devices for security purposes need to be able to remain inactive for several years, without reducing their reliability. Indeed, it is very likely that a burglary/violent threat will only happen (if ever) several years after installment of the device. It has been found that prior art fog-generating devices comprising pumps become unreliable over time, apparently due to blockage, corrosion and/or chemical resistance problems or other failure of these pumps when they are not regularly used. Although the pump-less variant of WO2008132113 already presents an improvement in that regard, it is not possible to fully exclude that the switch that regulates the release of the fog-generating fluid from the pre-pressurized reservoir would become micro-leaking or defective. Thus, there is a need for fog-generating devices that have reliable means that are stable over time, even if not used regularly, to transport the fog-generating fluid from the reservoir to the heat exchanger. In particular, a fog-generating device without moving parts or pre-pressurization that could get stuck over time would be very beneficial.
Furthermore, prior art fog generators are often “one-shot” devices, which require that the device is refilled in situ by a skilled technician, or require that the device is sent to the manufacturer for refilling. Especially for security purposes, it is not wanted that the device can not function for a substantial period until a technician has refilled it or until a replacement device has been sent and installed. In addition, such a process is time-, resource- and cost-intensive.
Further problems often associated with the prior art devices are the limited degree of freedom for orienting the device. Although orientation of the exit from where the fog is blown is often crucial, e.g. for concealing particular parts of the room in first instance, prior art devices don't allow much freedom as in certain positions the fog-generating device will simply not work, or fog-generating liquid will spill out of the reservoir, thereby damaging the device or leaving insufficient liquid in the reservoir for proper functioning.
For example, U.S. Pat. No. 6,087,935 discloses a smoke screen device containing a pyrotechnic device. However, it is very restricted in its orientation and tilting the device would result in absence of smoke production. In addition, the device is a “one-shot” and would need complete replacement or cumbersome refilling in a factory. Furthermore, smoke production will only be initiated after smoke fluid has been heated by a further pyrotechnic device, thereby slowing down the start of smoke exiting.
EP0726550 provides a smoke generator wherein a coil is heated by combustion of a mixture. Similar to U.S. Pat. No. 6,087,935 this slows down the start of smoke production and the device of EP0726550 contains a valve that blocks smoke fluid from entering the coil until it has been heated enough. In FIG. 4, EP0726550 also provides collection of combustion gasses to thrust liquid substances in the coil. However, similar to U.S. Pat. No. 6,087,935, the smoke generator of EP0726550 can not be oriented in any direction and smoke fluid may flow out of the reservoir and wet the reagent. Furthermore, the device is a “one-shot” device requiring replacement of the whole device after it functioned.
Thus, there is a continued need for fog-generating devices that allow to fill a room more quickly with fog, as well as by leading to a quicker start of fog generation as by expelling higher volumes of fog per second. In addition, there is a need for devices that allow a larger degree of freedom for orienting the devices during transport and installation. Furthermore, there is a need for fog-generating devices that can be easily set-up and does not require a skilled technician to come on-site or sending the device to a facility for refilling the device with fog-generating material after the device has been initiated.
It has been found that the fog-generating device and the removable housing of the present invention provide a solution to the above-mentioned problems.